Thats another thing.
Why is it that you can't see any part of Tobi's body? I mean his hands are pitch black when they show him picking up Sasori's ring. (Just like Pein, he has a thumb ring? LOL Coincidence?) The Tobi = Obito paradox had something along the lines of restoring Obito's body or something like that. The mask is just compensation for his missing sharingan eye (Does Tobi even have mangekyou? If so the same as Kakashi? Thats something to think about too.)
Think about it.
If Madara is truly immortal...he'd need an Uchiha body to merge his soul with...<_< I'm guessing he could've used Obito's battered body under the massive boulder. Hmmm, I will even go so far as to think that he found Obito's body 1 year before the Kyuubi was released (Kakashi, Obito and Rin were all 13 in Kakashi Gaiden, and Kakashi was 26 at the manga/anime's start as well leaving absent 1 year correct?)
Possible signs of Obito's own spirit had taken over through those instances with Deidara as well as being Zetsu's subordinate.